Prerequisites

An encrypted root filesystem or other filesystem that cannot be umounted while booted into the operating system.

Enough drive space to store a backup.

An Arch Linux (or other) live CD.

A few hours.

Note: As of late 2012 new tools have been added to cryptsetup to add or remove encryption to/from an existing file system. While they are still considered experimental, they may help considerably with such an effort. More information is available with man cryptsetup-reencrypt.

Boot into a Live Environment

Download and burn the latest archlive cd, reboot system and boot to cd.

Activate Partitions

Note About Different Setups

An example setup is shown here:

disk

ntfs

myvg(lvm)

ntfs

other os

cryptswap(lv)

cryptroot(lv)

Shared

luks

luks

swap

root(xfs)

The grey sections only add a frame of reference and can be disregarded.
The green partitions will be modified. Green text must match your system's setup.
The yellow partition will be used as storage space and may be changed at will.
In the example system:
myvg contains lvs called cryptroot and cryptswap. they are located at /dev/mapper/myvg_cryptroot and /dev/mapper/myvg_cryptswap. Upon boot, luks is used along with a few crypttab entries to create /dev/mapper/root and /dev/mapper/swap. Swap will not be unencrypted as part of this guide, as undoing the swap encryption does not require any complex backup or restoration.

The example system is not indicative of all systems. Different filesystems require different tools to effectively backup and restore their data. LVM can be ignored if not used.
XFS requires xfs_copy to ensure an effective backup and restore, DD is insufficient. DD may be used with ext2,3,and 4. (Someone please comment on jfs, reiserfs and reiser4fs)

Enter password.
Note: The only partition that will be operated on that should be mounted at this point is the backup partition. If a partition other than the backup partition is already mounted, it can be safely umounted it now.

Mounting backup space

Only if using NTFS to store the backup

# pacman -S ntfs-3g

The next step is important for backup storage.

# mount -t ntfs-3g -o rw /dev/sda5 /media/Shared

or use netcat to store the backup on a remote system

TODO: add netcat instructions.

Backup Data

Using xfs_copy:

xfs_copy -db /dev/mapper/root/media/Shared/backup_root.img

Note: -d flag preserves uuids and -b ensures direct IO is not attempted to any of the target files.

Using dd:

dd if=/dev/mapper/root of=/media/Shared/backup_root.img

Undo Encryption

Now the crucial moment, the point of no return if you will. Make sure you are ready to do this. If you plan to undo this later, you will have to almost start from scratch. You know how fun that is.

cryptsetup luksClose root
lvm lvremove myvg/cryptroot

Restore Data

We have to create a new logical volume to house our root filesystem, then we restore our filesystem.